The present invention relates to a method and apparatus for removing bromide from an electrolytic chlorination system.
It is well known to produce sodium hypochlorite from sodium chloride brine by converting the brine to sodium hypochlorite in an electrolyser. Sodium hypochlorite is used to treat potable water. Unfortunately, if the brine includes traces of bromide, the electrolyser causes the conversion of the bromide by oxidation to bromate. It is desirable to produce bromate-free sodium hypochlorite for the treatment of potable water as experiments have indicated that bromate may be carcinogenic.
It is an object of the present invention to provide a method and apparatus for removing bromide from an electrolytic chlorination system so as to obviate or mitigate the problem outlined above.
According to the present invention, there is provided a method for removing bromide from an electrolytic chlorination system in which brine is converted to sodium hypochlorite in an electrolyser, wherein the brine is fed to the electrolyser through a filter containing a medium capable of adsorbing bromine or hypobromous acid, and sodium hypochlorite is fed back from the electrolyser and mixed with the brine feed upstream of the filter to oxidize any bromide in the brine to bromine or hypobromous acid.
The present invention also provides an electrolyser for converting brine to sodium hypochlorite, means for feeding brine to the electrolyser, a filter through which the brine is fed to the electrolyser, the filter being capable of adsorbing bromine or hypobromous acid, and means for mixing sodium hypochlorite from the electrolyser with the brine upstream of the filter such that bromide in the brine is oxidized to bromine or hypobromous acid. Preferably hydrochloric acid is mixed with the brine upstream of the filter to maintain a low pH and thereby ensure effective oxidation of the bromide.